Turbocharger launch control

ABSTRACT

A method for launching a vehicle is disclosed. The method comprises, during operation with an idle engine speed prior to a pedal tip-in, increasing alternator and boost pressure while maintaining the idle engine speed, and decreasing alternator load responsive to the pedal tip-in. In this way, increased turbocharger output may be used to quickly accelerate the vehicle.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 13/234,348 filed Sep. 16, 2011, the entire contents of whichare incorporated herein by reference for all purposes.

FIELD

The present disclosure relates to a system and method for improvingvehicle launch with an engine including a turbocharger.

BACKGROUND AND SUMMARY

Turbo charging an engine allows the engine to provide power similar tothat of a larger displacement engine while engine pumping work ismaintained near the pumping work of a normally aspirated engine ofsimilar displacement. Thus, turbo charging can extend the operatingregion of an engine. Turbochargers function by compressing intake airvia a turbine operated by exhaust gas flow. During vehicle launchconditions, such as when accelerating from idle, minimal exhaust gasflow combined with increased load on the compressor results in a delayof the throttle response, referred to as turbo lag, leading to reducedengine power output.

One example approach to reducing turbo lag is described by Dixon et. al.in U.S. 2003/01106541. Therein, the likelihood that engine torque willneed to be boosted is estimated based on engine operating parameters,and an idle speed of the compressor is controlled as a function of thetorque boost likelihood.

However, the inventors herein have identified potential issues with theabove approach. Controlling the idle speed of the compressor requires aseparate motor to power the compressor. Operation of the motor reducesengine efficiency, thus wasting fuel, and requires extra enginepackaging space.

Thus, in one example, some of the above issues may be at least partlyaddressed by a vehicle launch method. The method comprises, at idlebefore pedal tip-in, increasing alternator load and boost pressure whilemaintaining idle speed, and responsive to pedal tip-in, decreasingalternator load.

In this way, before vehicle launch initiated by a pedal tip-in, thevehicle can be “pre-boosted,” or operated to increase boost to increaseengine power output during the launch. In one example, the pre-boostingincludes placing a maximum load on the alternator and retarding sparktiming. In some embodiments, pre-boosting may also include adjustingintake valve timing to best volumetric efficiency. By doing so, theengine air flow rate may be increased and the extra energy may be routedto the exhaust via the retarded spark timing and/or the extra energy maybe sent to electrical storage via the alternator. Exhaust output willthus increase, resulting in increased turbine spinning and increasedboost. Further, the load on the alternator may be reduced or completelyunloaded and spark timing may be advanced during the vehicle launch inorder to increase acceleration torque.

The present disclosure provides several advantages. By both pre-boostingthe engine and decreasing alternator load at vehicle launch, turbo lagcan be reduced. By reducing turbo lag without the inclusion of anadditional motor to power the turbine or compressor, engine efficiencycan be improved. Additionally, in hybrid vehicles, the extra energystored as a result of increasing the load on the alternator may bedischarged during or following the vehicle launch and used to power themotor, further increasing engine efficiency.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows a schematic diagram of a vehicle.

FIG. 2 shows a schematic diagram of an engine.

FIG. 3 shows a flow chart illustrating an example method forpre-boosting an engine according to an embodiment of the presentdisclosure.

FIG. 4 shows a flow chart illustrating an example method for launchingan engine according to an embodiment of the present disclosure.

FIGS. 5A and 5B show example engine operating parameter traces accordingto an embodiment of the present disclosure.

DETAILED DESCRIPTION

The present description is related to boosting a vehicle. In onenon-limiting example, the vehicle may be configured as illustrated inFIG. 1. Further, an engine as shown in FIG. 2 may be part of thevehicle. The engine and alternator of the vehicle may be controlledaccording to the methods of FIGS. 3 and 4 in order to produce the engineoperating parameters depicted in FIGS. 5A and 5B.

Referring now to FIG. 1, vehicle 100 includes wheels 102. Torque issupplied to wheels 102 via engine 10 and transmission 104. In someexamples, an electric motor or hydraulic motor may also provide torqueto wheels 102. Front end accessory drive (FEAD) 120 includes alternator110 and air conditioning (A/C) compressor 112. Alternator 110 and A/Ccompressor 112 may each be mechanically coupled to engine 10 via shaftor pulley 45, 47, or may be mechanically coupled to engine 10 via acommon shaft or pulley. Battery 108 and alternator 110 may provideelectrical power to various engine accessory components not shown inFIG. 1. Alternator 110 may be coupled to capacitor bank 114 via anelectronic interface 116 in order to store excess charge built up duringvarious operating modes of the engine. Capacitor bank 114 may compriseone or more capacitors arranged in parallel that receive and dischargecharge from alternator 110. In other embodiments, capacitor bank 114 mayinclude one or more capacitors arranged in series. Capacitor bank 114may receive change from alternator 110 in parallel, and discharge thecharge in series. In one embodiment, capacitor bank 114 may charge anddischarge voltage at a fixed voltage, such as 6, 12, or 24 volts, but inother embodiments may be configured to charge and discharge at fixed orvariable voltages other than 6, 12, or 24 volts.

In the embodiment depicted, capacitor bank 114 comprises onlycapacitors. However, in some embodiments, capacitor bank 114 maycomprise a battery/capacitor network, while in other embodiments, abattery bank may be utilized in place of capacitor bank 114. Controller12 includes instructions for controlling and receiving inputs fromalternator 110, A/C compressor 112, engine 10, and transmission 104.

Referring to FIG. 2, internal combustion engine 10, comprising aplurality of cylinders, one cylinder of which is shown in FIG. 2, iscontrolled by electronic engine controller 12. Engine 10 includescombustion chamber 230 and cylinder walls 232 with piston 236 positionedtherein and connected to crankshaft 240. Combustion chamber 230 is showncommunicating with intake manifold 244 and exhaust manifold 248 viarespective intake valve 252 and exhaust valve 254. Each intake andexhaust valve may be operated by an intake cam 251 and an exhaust cam253. Alternatively, one or more of the intake and exhaust valves may beoperated by an electromechanically controlled valve coil and armatureassembly. The position of intake cam 251 may be determined by intake camsensor 255. The position of exhaust cam 253 may be determined by exhaustcam sensor 257.

Fuel injector 266 is shown positioned to inject fuel directly intocylinder 230, which is known to those skilled in the art as directinjection. Alternatively, fuel may be injected to an intake port, whichis known to those skilled in the art as port injection. Fuel injector266 delivers liquid fuel in proportion to the pulse width of a signalfrom controller 12. Fuel is delivered to fuel injector 266 by a fuelsystem (not shown) including a fuel tank, fuel pump, and fuel rail (notshown). In addition, intake manifold 244 is shown communicating withoptional electronic throttle 262 which adjusts a position of throttleplate 264 to control air flow from air intake 242 to intake manifold244. In one example, a low pressure direct injection system may be used,where fuel pressure can be raised to approximately 20-30 bar.Alternatively, a high pressure, dual stage, fuel system may be used togenerate higher fuel pressures.

Distributorless ignition system 288 provides an ignition spark tocombustion chamber 230 via spark plug 292 in response to controller 12.Universal Exhaust Gas Oxygen (UEGO) sensor 226 is shown coupled toexhaust manifold 248 upstream of catalytic converter 270. Alternatively,a two-state exhaust gas oxygen sensor may be substituted for UEGO sensor226.

Engine 10 may further include a compression device such as aturbocharger or supercharger including at least a compressor 247arranged upstream of intake manifold 244. For a turbocharger, compressor247 may be at least partially driven by a turbine 245 (e.g., via a shaft249) arranged along exhaust passage 248. For a supercharger, compressor247 may be at least partially driven by the engine and/or an electricmachine, and may not include a turbine. Thus, the amount of compressionprovided to one or more cylinders of the engine via a turbocharger orsupercharger may be varied by controller 12 and further by adjusting oneor more of a wastegate 272 and/or compressor bypass valve 274. A chargeair cooler (not shown) may be included downstream from compressor 247and upstream of intake valve 252. Charge air cooler may be configured tocool gases that have been heated by compression via compressor 247, forexample.

Converter 270 can include multiple catalyst bricks, in one example. Inanother example, multiple emission control devices, each with multiplebricks, can be used. Converter 270 can be a three-way type catalyst inone example.

Controller 12 is shown in FIG. 2 as a conventional microcomputerincluding: microprocessor unit 202, input/output ports 204, read-onlymemory 206, random access memory 208, keep alive memory 210, and aconventional data bus. Controller 12 is shown receiving various signalsfrom sensors coupled to engine 10, in addition to those signalspreviously discussed, including: engine coolant temperature (ECT) fromtemperature sensor 216 coupled to cooling sleeve 214; a position sensor234 coupled to an accelerator pedal 213 for sensing force applied byfoot 212; a hydraulic brake pressure signal from sensor 233 coupled tohydraulic brake system 231; a measurement of engine manifold pressure(MAP) from pressure sensor 222 coupled to intake manifold 244; an engineposition sensor from a Hall effect sensor 218 sensing crankshaft 240position; a measurement of air mass entering the engine from sensor 220;and a measurement of throttle position from sensor 258. Barometricpressure may also be sensed (sensor not shown) for processing bycontroller 12. In a preferred aspect of the present description, engineposition sensor 218 produces a predetermined number of equally spacedpulses every revolution of the crankshaft from which engine speed (RPM)can be determined.

In some embodiments, the engine may be coupled to an electricmotor/battery system in a hybrid vehicle. The hybrid vehicle may have aparallel configuration, series configuration, or variation orcombinations thereof. Further, in some embodiments, other engineconfigurations may be employed, for example a diesel engine.

During operation, each cylinder within engine 10 typically undergoes afour stroke cycle: the cycle includes the intake stroke, compressionstroke, expansion stroke, and exhaust stroke. During the intake stroke,generally, the exhaust valve 254 closes and intake valve 252 opens. Airis introduced into combustion chamber 230 via intake manifold 244, andpiston 236 moves to the bottom of the cylinder so as to increase thevolume within combustion chamber 230. The position at which piston 236is near the bottom of the cylinder and at the end of its stroke (e.g.when combustion chamber 230 is at its largest volume) is typicallyreferred to by those of skill in the art as bottom dead center (BDC).During the compression stroke, intake valve 252 and exhaust valve 254are closed. Piston 236 moves toward the cylinder head so as to compressthe air within combustion chamber 230. The point at which piston 236 isat the end of its stroke and closest to the cylinder head (e.g. whencombustion chamber 230 is at its smallest volume) is typically referredto by those of skill in the art as top dead center (TDC). In a processhereinafter referred to as injection, fuel is introduced into thecombustion chamber. In a process hereinafter referred to as ignition,the injected fuel is ignited by known ignition means such as spark plug292, resulting in combustion. During the expansion stroke, the expandinggases push piston 236 back to BDC. Crankshaft 240 converts pistonmovement into a rotational torque of the rotary shaft. Finally, duringthe exhaust stroke, the exhaust valve 254 opens to release the combustedair-fuel mixture to exhaust manifold 248 and the piston returns to TDC.Note that the above is shown merely as an example, and that intake andexhaust valve opening and/or closing timings may vary, such as toprovide positive or negative valve overlap, late intake valve closing,or various other examples.

Turning to FIG. 3, a method 300 for pre-boosting an engine according toan embodiment of the disclosure is depicted. Method 300 may be carriedout by controller 12 in response to signals received from varioussensors, such as hydraulic brake pressure sensor 233. Method 300comprises, at 302, determining if catalyst temperature is above a firstthreshold. The first catalyst temperature threshold may be any suitabletemperature below which the catalyst may not be active. If the catalysttemperature is below the first threshold, the engine may be operatingunder cold start conditions and thus may operate with cold startparameters at 304. Cold start operating parameters may include directingexhaust output to the catalyst in order to heat the catalyst, and mayinclude adjusting intake cam timing to the best volumetric efficiencyposition, retarding spark timing, operating at rich air-fuel ratios,etc.

If catalyst temperature is above the first threshold, method 300proceeds to 306 to determine if catalyst temperature is below a secondthreshold. The second catalyst temperature threshold may be any suitabletemperature above which the catalyst may experience reduced activityand/or damage. If the catalyst temperature is not below the secondthreshold, method 300 proceeds to 320 to maintain non-pre boostoperating parameters. As the pre-boost conditions may increase catalysttemperature, if the catalyst temperature is already relatively high, thecatalyst may experience damage during the pre-boost, and thus the enginemay not be pre-boosted when catalyst temperature is above the threshold.

If catalyst temperature is below the second threshold, method 300proceeds to 308 to determine if hydraulic brake pressure has dropped bya threshold amount. For example, when a vehicle operator releases thebrake pedal, the hydraulic brake pressure will drop. Detecting change inhydraulic brake pressure rather than change in brake pedal positionenables a more rapid detection of change in brake status. The drop inpressure threshold amount may be any suitable amount that indicates theoperator intends to fully release the brake pedal. In one embodiment,the threshold amount may be a drop of 50%, or it may be a drop of asuitable amount over a particular time period.

If it is determined at 308 that hydraulic brake pressure has dropped bya threshold amount, method 300 proceeds to 310 to enable the pre-boostoperation. The drop in hydraulic brake pressure may indicate theoperator has released the brake pedal in order to accelerate and enablevehicle movement. In turbocharged engines, acceleration following idleconditions (such as when a vehicle starts to move following a stop at astoplight) can often result in an acceleration lag due to the lack ofexhaust output to spin the turbine of the turbocharger. The pre-boost isenabled following brake pedal release in order to generate extra exhaustoutput to spin the turbine, and increase acceleration torque for asubsequent vehicle launch. In order to generate increased turbinespinning, airflow through the engine may be increased. Thus, moreexhaust flow will occur, and the turbine can spin with increased speed,driving the compressor to compress the increased airflow into theengine. However, as the pre-boost is performed in response to anoperator releasing the brake pedal and before the engine is launched,inadvertent acceleration as a result of the increased airflow may occur.To avoid this, a number of operations are performed during the pre-boostmode to control engine speed. Thus, the pre-boost includes a variety ofactions to increase boost while controlling engine speed. Further, thepre-boost includes actions to optimize a subsequent vehicle launch.

Enabling the pre-boost includes closing a wastegate and compressorbypass valve (CBV) at 312. When open, the wastegate allows exhaust tobypass the turbine, and the CBV allows intake air to bypass thecompressor. Both the wastegate and CBV can be controlled to modulate theamount of boost provided to the engine. By closing the wastegate, moreexhaust will be funneled to the turbine to maximize turbine output.Further, by closing the CBV, throttle inlet pressure can be increased.The wastegate may have a set point based on engine speed and load, forexample. During the pre-boost, this set point may be adjusted toincrease boost pressure. Under some conditions, the wastegate and/or CBVmay be fully closed, while under other conditions, the wastegate and/orCBV may be left partially open to direct most of the exhaust power tothe turbocharger while allowing some exhaust and/or intake air to bypassthe turbocharger.

Increased load may be placed on one or more front end accessory drive(FEAD) components at 314. By increasing the load to the FEAD, enginespeed can be controlled. For example, the A/C compressor may be operatedsuch that compressor head pressure is at a maximum safe pressure.Additionally, the alternator may be operated at increased load byincreasing the alternator charging voltage, for example by adjusting thealternator field. In one embodiment, the alternator load may beincreased to maximum alternator load. In other embodiment, the degree ofincrease in the alternator load may be adjusted based on variousconditions, such as the exhaust gas temperature, the boost level beforeincreasing the alternator load, and others. For example, if the boostlevel before increasing the alternator load is at or above atmosphericpressure, less alternator load may be added. Further, as the load placedon the alternator may be limited by the charging capacity of the batteryand/or electric power demand of the vehicle accessories, an extra chargestorage apparatus may be coupled to the alternator to handle the extraload. For example, one or more capacitors may be coupled to thealternator to store extra charge generated during the pre-boostoperation. In other embodiments, one or more additional batteries may becoupled to the alternator.

Enabling the pre-boost also includes retarding spark timing at 316 andadvancing intake cam timing at 318. By retarding spark timing, powergenerated during combustion may be limited so that excess torque andengine speed can be avoided. Additionally, intake cam timing may beadvanced to the best volumetric efficiency position during thepre-boost. Because there may be a lag associated with advancing camtiming, advancing during the pre-boost will enable the cam timing to bein the optimal position during a subsequent vehicle launch.

If it is determined at 308 that hydraulic brake pressure has not droppedby a threshold amount, for example if the vehicle is still stopped, orif it is moving without the operator using the brake pedal, method 300proceeds to 320 to maintain non-pre-boost engine operating parameters.Non-pre-boost operating parameters include opening the wastegate and CBVin response to exhaust pressure at 322. Unlike in the pre-boost mode,the non-pre-boost conditions include allowing the wastegate and CBV toopen, dependent upon engine speed and load, exhaust pressure etc., sothat air movement through the turbocharger can be controlled to avoidexcess boost that can damage engine components.

The non-pre-boost operating parameters also include loading thealternator based on battery charge state and/or accessory componentdemand at 324. As the alternator converts engine mechanical energy intoelectrical energy for storage in the battery, the load on the alternatormay be based on the current charge state of the battery, and thus may behigher if the battery is low on charge or may be lower if the battery isfully charged. Further, the alternator provides electricity to certainvehicle accessories such as a radio when the charge from the battery isnot enough to operate them, and so alternator load may also be based onaccessory demand. Similarly, the A/C compressor load may be based on A/Cdemand at 326.

Non-pre-boost operating parameters include maintaining spark atoptimized timing for the current operating conditions at 328. In someembodiments, this may include maintaining spark timing at MBT. Likewise,at 330, the non-pre-boost operating parameters include maintain intakecam timing at the optimized timing for the current operating conditions,which in some embodiments may not include the best volumetric efficiencyposition.

Thus, method 300 provides for determining if a vehicle may bepre-boosted, and if so, carrying out various actions that enable extraengine boost while limiting engine speed. In some circumstances,following the pre-boost, the vehicle will start to launch whereby anoperator of the vehicle will accelerate to launch the vehicle. FIG. 4depicts a method 400 for launching a vehicle according to an embodimentof the present disclosure. Method 400 may be carried out by controller12.

Method 400 comprises, at 402, determining if the engine is currentlyoperating in pre-boost, such as the pre-boost conditions described abovewith respect to FIG. 3. If the answer is no, method 400 proceeds to 404to maintain the current engine operating parameters, and the methodends. If the answer at 402 is yes, method 400 proceeds to 406 todetermine if an accelerator pedal has been depressed past a thresholdlevel. Accelerator pedal position may be determined by sensor 234. Thethreshold level may be any suitable level that indicates an operatorintent to accelerate the vehicle at relatively fast rate, e.g., thethreshold position may be depressed by 20%, by 50%, etc. In otherembodiments, the threshold pedal position may be any depressed position.

If the accelerator pedal has not been depressed past a threshold level,method 400 proceeds to 408 to determine if a predetermined amount oftime has elapsed since the initiation of the pre-boost. Thepredetermined time may be any suitable time that indicates the operatoris not intending to immediately accelerate the vehicle, such as onesecond, two seconds, etc. If the predetermined time has not elapsed,current engine operating parameters are maintained at 410 in order tocontinue to operate the vehicle in pre-boost conditions, and the methodreturns to reassess if the engine is operating in pre-boost and if thepedal position is subsequently depressed. If the predetermined amount oftime has elapsed since the pre-boost was initiated, method 400 proceedsto 418 to resume non-pre boost operating parameters, such as thosedescribed with respect to FIG. 3, and subsequently exits.

However, if at 406 it is determined that the accelerator pedal positionis past the threshold, method 400 proceeds to 412 to launch the vehicle.During the pre-boost, the engine is operated with a number of parametersto increase airflow through the turbine while controlling engine speed.During the launch, the parameters to control engine speed are adjustedso that the vehicle can accelerate. Accordingly, the alternator and A/Ccompressor are unloaded at 414 and spark timing is advanced at 416. Theother operating parameters initiated during the pre-boost, includingwastegate and CBV position and intake cam timing, are maintained duringthe vehicle launch. Following the engine launch, for example, after apredetermined amount of time has elapsed, or after the engine speedsteadies, method 400 proceeds to 418 to resume non-pre boost operatingparameters. Non-pre-boost operating parameters may include thenon-pre-boost operating parameters described above with respect to FIG.3, and may also include discharging the excess charge stored in thecapacitor bank during the pre-boost.

FIGS. 5A and 5B depict example engine operating traces during executionof the above described methods. FIG. 5A illustrates example brakepressure 510, accelerator pedal position 520, wastegate position 530,and throttle inlet pressure 540 traces, while FIG. 5B illustratesexample throttle 550, engine speed 560, spark timing 570, and alternatorload 580 traces. At the start of the traces, brake pressure is high,indicating the brake is being depressed, and the accelerator pedalposition is at zero. Additionally, the engine speed is low, and thus thevehicle is in idle-in-drive, whereby the vehicle is idling while theoperating depresses the brake. The wastegate is at its non-pre-boost setpoint (in this embodiment it is partially open), TIP is low (e.g. atbarometric pressure), spark timing is at MBT, and the alternator isoperating under low load. At 502, the operator releases the brake andbrake pressure drops below a threshold amount. The vehicle then beginsthe pre-boost by adjusting the set point of the wastegate (and, in someembodiments, the compressor bypass valve, not shown in FIG. 5A or 5B) sothat more exhaust is directed to the turbine. Spark timing is retarded,one or more loads are placed on the FEAD (e.g., the alternator load isincreased), and the pre-boost is indicated by the increase in the TIP.While the throttle opens some to admit more air into the engine, itremains relatively steady in order to control engine speed.

At 504, the operator depresses the accelerator pedal past a thresholdposition and the vehicle starts to launch. Accordingly, spark timing isadvanced, engine speed increases, the throttle opens, the load placed onthe alternator is reduced, and TIP pressure increases. While in theembodiment depicted, the load on the alternator is decreased but yet asmall load is still present during the launch, in some embodiments, theload on the alternator may be reduced such that there is no load on thealternator during the launch. In order to increase the TIP, thewastegate (and compressor bypass valve) remains at the restricted setpoint that it was adjusted to during the pre-boost.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific methods and routines described herein may represent one ormore of any number of processing strategies such as event-driven,interrupt-driven, multi-tasking, multi-threading, and the like. As such,various acts, operations, or functions illustrated may be performed inthe sequence illustrated, in parallel, or in some cases omitted.Likewise, the order of processing is not necessarily required to achievethe features and advantages of the example embodiments described herein,but is provided for ease of illustration and description. One or more ofthe illustrated acts or functions may be repeatedly performed dependingon the particular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and methods disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

The invention claimed is:
 1. A vehicle launch method, comprising: duringoperation with an idle engine speed prior to an accelerator pedaltip-in, increasing alternator load and boost pressure via aturbocharger, and operating with retarded spark timing, whilemaintaining the idle engine speed; and responsive to the acceleratorpedal tip-in, decreasing alternator load and advancing spark timing. 2.The method of claim 1, wherein increasing alternator load and boostpressure while maintaining the idle engine speed are performed inresponse to a drop in hydraulic brake pressure exceeding a threshold. 3.The method of claim 1, wherein the pedal tip-in comprises an acceleratorpedal being depressed past a threshold level.
 4. The method of claim 1,further comprising, during the operation with the idle engine speedprior to the pedal tip-in, closing a wastegate and compressor bypassvalve.
 5. The method of claim 1, further comprising, during theoperation with the idle engine speed prior to the pedal tip-in,increasing a load to an air conditioning compressor.
 6. The method ofclaim 5, further comprising, responsive to the pedal tip-in, decreasingthe load on the air conditioning compressor.
 7. The method of claim 1,further comprising, during the operation with the idle engine speedprior to the pedal tip-in, advancing intake cam timing.
 8. The method ofclaim 7, further comprising, responsive to the pedal tip-in, advancingspark timing.
 9. A method for controlling a vehicle, comprising: priorto a vehicle launch while at idle engine speed and responsive tocatalyst temperature below a temperature that causes damage, in responseto a drop in hydraulic brake pressure, increasing boost pressure via aturbocharger above barometric pressure while increasing engine airflow,increasing an engine accessory load, advancing intake cam timing, andmaintaining idle engine speed with retarded spark timing; and launchingthe vehicle from the idle engine speed in response to an acceleratorpedal being depressed past a threshold level by reducing the engineaccessory load.
 10. The method of claim 9, wherein launching the vehiclefurther comprises advancing spark.
 11. The method of claim 9, furthercomprising closing a wastegate and a compressor bypass valve prior tothe vehicle launch.
 12. The method of claim 9, wherein increasing theaccessory load on the engine further comprises increasing a load placedon an alternator prior to the vehicle launch.
 13. The method of claim12, wherein reducing an accessory load on the engine further comprisesdecreasing the load placed on the alternator.
 14. The method of claim12, wherein voltage produced as a result of the increased load on thealternator is stored in a capacitor bank coupled to the alternator andwherein the stored voltage is subsequently discharged following thevehicle launch.
 15. A vehicle launch method, comprising: during an idleengine operation: increasing alternator load and boost pressure via aturbocharger by closing a wastegate and a compressor bypass valve whilemaintaining idle engine speed; storing voltage produced as a result ofthe increased load on the alternator in a capacitor bank coupled to thealternator; and responsive to an accelerator pedal tip-in from idleengine speed, decreasing alternator load.
 16. The method of claim 15,further comprising discharging the stored voltage during engineoperation following the pedal tip-in.
 17. The method of claim 15,wherein maintaining the idle engine speed further comprises retardingspark timing.